I ordered it online because I liked the 15mm thickness. It arrived folded in half and wrapped in plastic. As a result, the center part of the rolled-up part was the most compressed and flattened. The outer part of the rolled-up part, which was less compressed, was 15mm, and the flattened part was 2mm. Will this flattened part return to its original shape? The instructions didn't mention anything about this, and when I called to ask about it, I was told to wait and see for a couple of days. I hung it up on a pipe hanger in the same way you would hang up a futon, and waited and saw what would happen. The part that had been less compressed certainly did return to its original thickness over time. However, the part that had been flattened to 2mm hardly expanded at all. So, I took a gamble and pulled on the 2mm part from both sides. Be careful not to pull too hard, as you might tear the sponge-like part inside! As a result, it was usable without any problems. I would like them to clearly state that there is a possibility that it will be crushed in the packaging. If you don't just wait idly for a couple of days, but instead open up the crushed part, it will recover more quickly. As there is a possibility that you won't be able to use it immediately after buying it, I recommend that you buy it with plenty of time to spare.